FakeFile() and to assign() or not to assign()

Is there a particular reason this doesn't work:

Pike v7.8 release 127 running Hilfe v3.5 (Incremental Pike Frontend)

Stdio.FILE in; (in=Stdio.FILE())->assign(Stdio.FakeFile("foo\nbar\n"));

Stdio.File(): not open. /usr/local/pike/7.8.127/lib/modules/Stdio.pmod/module.pmod:1490: Stdio.FILE(0, 0, 777 /* fd=-1 */)->set_read_callback(0) /usr/local/pike/7.8.127/lib/modules/Stdio.pmod/module.pmod:1192: Stdio.FILE(0, 0, 777 /* fd=-1 */)->set_read_callback(0) /usr/local/pike/7.8.127/lib/modules/Stdio.pmod/module.pmod:727: Stdio.FILE(0, 0, 777 /* fd=-1 */)->assign(Stdio.FakeFile(8,"rw")) /usr/local/pike/7.8.127/lib/modules/Stdio.pmod/module.pmod:1776: Stdio.FILE(0, 0, 777 /* fd=-1 */)->assign(@0=Stdio.FakeFile(8,"rw"))